The proposed research is aimed at increasing current knowledge of hyperactive children's disturbances in attention and the beneficial effects of methylphenidate on this disorder. The research will examine the controversy on whether hyperactives' visual evoked responses are larger than normal children's and the effects of methylphenidate on this abnormality. The major focus of this work will be on hyperactives' performance and late positive component of the evoked response (LPC) during selective attention. We seek to extend our previous findings that under sustained attention, hyperactives display worse performance and lower LPC amplitude than normals and that methylphenidate ameliorates these abnormalities. We plan to extend these findings to newly diagnosed patients who have not been treated with stimulants and to relate improvement in LPC amplitude and performance to clinical response to methylphenidate. We will employ a more difficult experimental task to maximize differences between hyperactives and normals. Because this version of the task includes experimental stimuli of varied levels of relevance, we will be able to perform a more sensitive examination of the effects of methylphenidate on LPC amplitude as a function of experimental significance. The study will include 50 newly diagnosed hyperactives and 50 normal children of comparable age and sex. There will be two identical sessions involving visual stimulation at multiple levels of intensity and the X and B-X versions of the Continuous Performance Task. Prior to each session, hyperactives will be administered, in counterbalanced order and blind fashion, methylphenidate or placebo. Normals will not receive any drug. Subsequently, hyperactives will undergo a 6-week clinical trial of methylphenidate followed by a blind 4-day placebo-drug test. Teachers' and parents' ratings during this period will be used to objectively define response to medication. This work will aid in understanding the nature of hyperactives' attentional disorder and provide clues on the aspects of these disorders that are ameliorated by methylphenidate.